This invention relates generally to height adjustable portions of chairs, and particularly, to a height adjustment mechanism for a movable portion of a chair. More particularly, the invention relates to an adjustable armrest assembly. However, the height adjustment mechanism may also be used for other adjustable portions of a chair, including, for example, the back rest, or potentially even the seat.
A wide variety of adjustable office chairs are presently available. In an attempt to adapt the chair to a particular user or task, various adjustment mechanisms have been provided. Such chairs may, for example, include vertically adjustable seat height mechanisms, swivel tilt mechanisms, and vertically adjustable height mechanisms for armrests and backrests.
Prior art armrest and backrest height adjustment mechanisms are available in various forms. In some, manually operable mechanisms, such as using buttons or handles, which require manipulation of a release/lock member prior to being able to adjust the arm or back rest portion. Examples of adjustable height armrests are described in U.S. Pat. No. 6,394,553 to McAllister, et al, and U.S. Pat. No. 5,393,125 to Watson, et al.
Prior art mechanisms for height adjustable chair backrests are known which can operate xe2x80x9cautomatically,xe2x80x9d in the sense that no release or lock member need be manually operated prior to attempting to move the adjustable portion of the chair. In these types of mechanisms, the adjustable backrest can be raised or lowered and the adjustment mechanism operates automatically to maintain the backrest in the adjusted position.
One example of such an xe2x80x9cautomaticxe2x80x9d vertical adjustment mechanism for a chair backrest is described in U.S. Pat. No. 4,749,230 to Tornero. The mechanism described in this patent generally comprises two guided and slidably interlocking plates and one lock pin. The lock pin is free to move within a sinus-shaped slot defined within one plate and forced therewith from one locked position to a stand-by position, or to an unlocked position by the cam action of any of a plurality of notches and inclined surfaces of a slotted cam contained on the other plate. According to Tornero, this mechanism is characterized by the absence of springs or other supplementary biasing means. Instead of a spring member, the position of the pin in the sinus-shaped slot is controlled by a series of camming surfaces similar to the notches and inclined surfaces of the cooperating slotted cam plate. However, there is nothing which retains the pin in any of the positions other than the shape of the slot. This particular means of controlling the pin using the shape of the slot can have disadvantages. For example, rapid or overly forceful adjustment of the backrest could displace the lock pin to an unlocked position, which would require moving the backrest to the full up position in order to re-set the lock pin in a position where the adjustment process could be repeated. In addition, the shape of the slot holds the pin in each of the three positions, rather than using springs or gravity. Thus, camming surfaces, activated by manual force, are employed to move the pin between the three positions defined by the shape of the slot. Another potential disadvantage of this type of design can be in regard to securing the position of the pin in a particular position in the slot to prevent the pin from inadvertently dislodging from the notch in the slotted cam plate, such as, for example, by excessive or rapid application of force to the backrest, sudden movement, or jarring of the backrest or chair.
Another example of an xe2x80x9cautomaticxe2x80x9d vertical adjustment mechanism for a chair backrest is described in U.S. Pat. No. 5,037,158 to Crawford (xe2x80x9cthe ""158 patentxe2x80x9d), assigned to the assignee of the present invention. The mechanism described in the ""158 patent comprises a vertical member containing a centrally located camming slot that is elongated in a vertical direction and has a series of notches located along one side and a smooth surface located along the other side. The top and bottom of the camming slot contain downwardly directed camming surfaces. A back adjustment plate includes a centrally located horizontal slot and a guide pin positioned within the slot supported by an S-shaped leaf spring. When the guide pin is moved in either direction away from the central axis of the slot, the leaf spring causes the pin to be biased in the direction that the pin has been moved away from. In order to raise the chair back relative to the seat, the chair back is grasped by the user and pulled in an upward direction whereupon the pin is urged in the direction of the notches and registers in each of the notches as the chair back is moved in an upward direction. In order to lower the seat back, the seat back is raised fully which causes the pin to be urged in the direction of the smooth surface. As the pin rides along the upper surface in the direction of the smooth surface, the pin will pass the halfway point in the slot and spring will urge the pin in the direction of the surface. One advantage of this particular mechanism can be greater smoothness of operation (and thus less force to adjust the backrest) because the slot in which the pin rides is smooth, since no camming surfaces are used to control the position of the pin therein. Other advantages can include reliability, in that the leaf spring can more positively control the position of the pin in the slot, making it more likely that the pin will be maintained in the desired position, and less likely to dislodge from that position, for example, such as by sudden movement or jarring of the chair. However, the need for the leaf spring member itself can be a disadvantage, because it is an additional small moving part, and it increases the cost of the mechanism.
Consequently, there is a need for a height adjustment mechanism for adjustable portions of a chair, specifically the armrest, but also potentially the backrest or seat, wherein the height adjustment mechanism is simple, easy to use, and at the same time highly reliable and less costly. The present invention is directed toward filling that need.
An adjustable armrest assembly is provided comprising a fixed member having a chair attachment portion and a housing portion, a vertically adjustable member having an armrest portion and a post portion, with the post portion having a lower end thereof slidably disposed in the housing portion, and the vertically adjustable member is selectively movable between a fully raised position, a fully lowered position, and at least one intermediate position via a height adjustment mechanism.
The height adjustment mechanism comprises a first member having a housing portion and a support portion, a second vertically adjustable member having an upper end and a lower end, the lower end being slidably disposed in the housing portion, and the lower end further having a camming slot formed therein. The camming slot has a plurality of notches on one side thereof and a generally planar surface on an opposing side. A sleeve member can be provided in between the housing and the post, with an inner surface of the sleeve member adjacent opposite sides of the camming slot. The sleeve member can have an angled slot formed in the inner surface thereof on opposite sides of the camming slot, such that a locking pin can be operably positioned through both the camming and angled slots, with opposite ends of the locking pin slidably captured in the angled slot. A bushing member can be provided in the sleeve member such that the bushing member projects at least partially into the angled slot such that upper and lower regions of the angled slot are defined by the bushing member. The upper region of the angled slot is adjacent the generally planar surface of the camming slot, whereas the lower region is adjacent the plurality of notches. The camming slot further has top and bottom surfaces, wherein the top surface forces the locking pin across the bushing member into the lower region of the angled slot at the fully lowered position, and the bottom surface forces the locking pin across the bushing member into the upper region of the angled slot at the fully raised position. The locking pin being maintained in either the upper or lower regions by the bushing member until otherwise caused to move across the bushing member by the bottom or top surface. When the locking pin is maintained in the lower region of the angled slot, gravity urges the locking pin toward the plurality of notches, such that the locking pin is urged into one of the plurality of notches when such one of the notches becomes aligned with the lower region of the angled slot, as will occur responsive to upward vertical movement of the armrest. The armrest is held at a height corresponding to the notch occupied by the locking pin. The locking pin is moveable from whichever notch is occupied responsive to further upward vertical movement of the armrest, up to the fully raised position, at which the locking pin will be urged away, by the bottom surface of the camming slot, from the notched side of the camming slot into the upper region of the angled slot by the bottom surface of the camming slot. The locking pin will be maintained, by the bushing member, in the second region of the angled slot until the armrest is moved to the fully lowered position, which will result in the top surface of the camming slot moving the locking pin back across the bushing member into the lower region of the angled slot. At this point, the locking pin is positioned to repeat the selectable vertical adjustment process by upward vertical movement of the armrest.
The adjustable armrest assembly/height adjustment mechanism, can also be provided with one or more compression members disposed between the outer surface of the sleeve member and the inside surface of the housing portion. The sleeve member can also be a pair of sleeve members and the bushing member can be a pair of bushing members, each associated with a respective sleeve member. The bushing members can partially project only into the angled slot formed in the sleeve member, and not into the camming slot, such that the bushing members contact only the ends of the locking pin which are slidably captured in the angled slot.
The adjustable armrest assembly of can further comprise an arm pad which is securable to the armrest portion and has a resiliently flexible insert member. The resiliently flexible insert member can be a thin plate-like member having a width and length substantially the same as the arm pad. The thin plate-like member can be made from spring steel, or an appropriate plastic or other material having resiliently flexible properties.
Other details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying drawing figures of certain embodiments thereof.